Hi The manpage regex(7) is explcitly mentioned in the new LPI objectives, but in preparation to make study material for this subject, I feel a strong sense of repulsion to even mention this page, as I cannot understand what anyone would learn from it... Probably the source of the problem lies with POSIX.2, as this has apparently an ambiguous definition of the "extended" regular expressions and (IMO erroneously) defines the basic regular expressions as obsolete, though they are used in many many programs, including grep, vim, sed, etc. I may be wrong, but when I see so many (!)'s in the manpage, indicating that this is not implemented equally, the whole definition is broken and there is no such thing as "extended" or "modern" REs, but a bunch of varying implementations of roughly similar extended RE rules. Also, if I interpret the page correctly, "modern" REs don't have backreferences? They are mentioned as a new item for BASIC REs. While they are bothersome to use, backreference are useful and would be missed in an extended RE implementation without them. (certainly, egrep /did/ implement them) To me, the "modern" REs are a simplification of the syntax with bounds and () enclosures without preceding '\'s and adding a bunch of weirdly long character class notations that I doubt anyone uses frequently, since they are too long to type and remember ([. [= [:) If I were on the POSIX committee, I'd propose perl REs as the next "modern" RE, but I'd not obsolete the basic RE at all, because in 95% of the uses they are sufficient. Perl REs are easy to type, well documented and powerful. Also implementations already exist and are very well tested on probably all Unix platforms. Anyway, the point of this e-mail: - the current page is awful, hard to read and ambiguous - the implied POSIX decision to obsolete basic REs is bad - I would not recommend this manpage to anyone trying to understand REs If possible I'd like to change the world ;-) but failing that, a less ambiguous (and easier to read) version of the regex(7) manpage would be greatly appreciated! Cheers Simon PS, speaking on personal title, not for my employer AT Computing PPS, I'd love to be proved wrong on any of my statements, so please correct me if I'm wrong. -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
